Thanks: http://www.mssqlcity.com/Articles/KnowHow/Textcopy.htm
You should insert something into text/image column before copy text/image into it. This value should not be null. You should write for a blob:
INSERT INTO [dbo].[images] VALUES ('1', 0x0, null)
Or of course a string for a text column.
This is the output of textcopy /?
Copies a single text or image value into or out of SQL Server. The value is a specified text or image 'column' of a single row (specified by the "where clause") of the specified 'table'. If the direction is IN (/I) then the data from the specified 'file' is copied into SQL Server, replacing the existing text or image value. If the direction is OUT (/O) then the text or image value is copied from SQL Server into the specified 'file', replacing any existing file. TEXTCOPY [/S [sqlserver]] [/U [login]] [/P [password]] [/D [database]] [/T table] [/C column] [/W"where clause"] [/F file] [{/I | /O}] [/K chunksize] [/Z] [/?] /S sqlserver The SQL Server to connect to. If 'sqlserver' is not specified, the local SQL Server is used. /U login The login to connect with. If 'login' is not specified, a trusted connection will be used. /P password The password for 'login'. If 'password' is not specified, a NULL password will be used. /D database The database that contains the table with the text or image data. If 'database' is not specified, the default database of 'login' is used. /T table The table that contains the text or image value. /C column The text or image column of 'table'. /W "where clause" A complete where clause (including the WHERE keyword) that specifies a single row of 'table'. /F file The file name. /I Copy text or image value into SQL Server from 'file'. /O Copy text or image value out of SQL Server into 'file'. /K chunksize Size of the data transfer buffer in bytes. Minimum value is 1024 bytes, default value is 4096 bytes. /Z Display debug information while running. /? Display this usage information and exit. You will be prompted for any required options you did not specify.